The present invention relates to a battery pack for mounting a battery on a vehicle such as an electric vehicle or a hybrid vehicle, and more particularly, to a battery pack which is disposed under a floor of a vehicle body and contains a plurality of battery modules.
In an electric vehicle which uses an electric motor as a driving source, or a hybrid vehicle which uses an electric motor and an engine as driving sources, a battery pack which contains a battery for supplying electric power to the motor is mounted.
The battery pack contains a plurality of battery modules in a battery containing member such as a battery pack tray.
As an example of the related art, a power supply device including a plurality of battery modules which are contained in a battery pack is disclosed in JP-A-2009-4323.
In JP-A-2009-4323, it is disclosed that a first battery group B1 is formed by electrically connecting a plurality of battery cells in series by means of bus bars (electrically connecting members), and a second battery group B2 is formed by connecting a plurality of battery cells in the same manner, and these battery groups are further connected by means of bus bars, thereby to form the power supply device.
In JP-A-2011-86634, it is disclosed that a plurality of battery cells are connected in series by means of bus bars thereby to form a battery module.
In order to form the power supply device by electrically connecting a plurality of the battery cells in series by means of the bus bars to form the battery modules, and further, by connecting these battery modules by means of the bus bars, as described in JP-A-2009-4323 and JP-A-2011-86634, it is necessary for the bus bars to protrude above the battery modules or to be connected to terminals of the adjacent battery modules by going around outside of the battery modules. Therefore, a space for installing the bus bars for the serial connection is required in the battery pack for containing a plurality of the battery modules, and so, it has been difficult to contain the battery modules in a compact manner.
An example of the serial connection of the battery modules by arranging the bus bars above the battery modules and between the adjacent battery modules is shown in FIG. 8. In FIG. 8, battery modules 01a to 01e which are formed by connecting a plurality of battery cells in series by means of inter-cell bus bars (not shown) are disposed in a tray 02 of a battery pack to be mounted on a vehicle.
The battery modules 01a to 01e are arranged in such a manner that their electrodes are positioned in the same direction in a vehicle anteroposterior direction. For this reason, in order to connect all the battery modules 01a to 01e in series, their positive electrodes and negative electrodes must be connected, by installing bus bars 03 so as to go across the battery modules 01a to 01e, and so as to pass through spaces between the adjacent battery modules.
In case where the spaces between the battery modules 01a to 01e and surrounding spaces are utilized, the bus bars need not protrude above the battery modules to go across them. However, in this case, there occurs such a problem that the battery pack for containing the battery modules is upsized, because the surrounding spaces must be secured.
Moreover, it is desired for the battery pack provided under the floor of the vehicle body to have the possible smallest height in a vertical direction, for the purpose of securing both a space for passengers and a height of the vehicle from the ground.